Siliceous composition and method for manufacturing the same



Dec. 28, 1954 F. L. SHEA, JR., ETAL SILICEOUS COMPOSITION AND METHOD FOR MANUFACTURING THE SAME Filed Jan. 12, 1950 3 Sheets-Sheet 1 ZOO M -O ILO TIME IN MINUTES 'WWOV NI NOLLVILBNHd JNVENTORJ" FREDERICK L..SHEA JR. HARRY .Hsu

ATTORNEY Dec. 28, 1954 F. L. SHEA, JR. ETAL 2,698,256 SILICEOUS COMPOSITION AND METHOD FOR MANUFACTURING THE SAME 3 Sheets-Sheet 2 Filed Jan. 12, 1950 o 0 w m 4 TIME IN MINUTES -'-i- TiME m MINUTES INVENTORY FREDERICK L-SHEA JR. HARRY L, HSU

A TZ'URNEY Dec. 28, 1954 SHEA JR.

ET AL SILICEOUS COMPOSITION AND METHOD FOR MANUFACTURING THE SAME Fzled Jan. 12, 1950 3 Sheets-Sheet 3 INVENTORS Fkeosmcx L.5HEAJR. HARRY n..usu

United States Patent SILICEOUS COMPOSITION AND METHOD FOR MANUFACTURING THE SAME Frederick L. Shea, Jr., Chicago, and Harry L. Hsu, Evanston, Ill., assignors to Great Lakes Carbon Corporation, Morton Grove, 11]., a corporation of Delaware Application January 12, 1950, Serial No. 138,253

11 Claims. (Cl. 106-308) This invention relates to the manufacture of light weight siliceous materials. More particularly, the invention relates to a method for chemically converting silica in its various forms to a form which is more reactive chemically and which has properties which render it particularly amenable to the manufacture of light weight heat-insulating materials of high strength.

The manufacture of high temperature heat insulation has been. more or less restricted to the utilization of siliceous materials due to the fact that magnesia types of insulation disintegrate rapidly or check severely at temperatures upwards of 1000 F. For this reason, the industry has relied extensively upon the use of various forms of silica which are reacted with binders, for example those of the calcareous type such as lime, Portland cement, shale, etc. The practice of manufacturing such insulation is quite old in the art as evidenced by a patent issued to Brown, U. S. 311,287. The technique of preparing such insulation from diatomaceous earth and calcareous binders has been somewhat improved, the main emphasis being laid upon the preparation of insulatign blocks or slabs of low density and high mechanical strength. These obiects have in part been achieved by adding asbestos fiber to the diatomaceous earth-calcareous mixture. It has also been proposed to add certain colloids or dispersing agents to an aqueous slurry of the reactants in order to effect improved stability of the reaction mixture in the period during which the diatomaceous earth reacts With the binder to form a pre--hardened body. It has been possible to produce siliceous insulation blocks or slabs having a density of about 12 to 30 lbs/cu. ft. with a modulus of rupture between about 30 and'150 lbs/sq. in., but this is only achieved by employing highly specialized forms of asbestos fibre.

The preliminary reaction between diatomaceous earth or other siliceous materials and a calcareous binder is usually carried out in such a manner that the reactive mix will not set up or harden before the mixture is placed in molds of suitable shape and design. Following the preset or hardening, the resulting siliceous bodies are then heated, usually by means of an autoclave, at temperatures in excess of 100 C. to further accelerate and increase the extent of the reaction between the siliceous material and the binder. It is the usual practice to preliminarily react the siliceous material and binder in the presence of colloids or agents for suspending the reactants for a period of time approximating two hours at temperatures of the order of 80 to 100 C. Following this preliminary reaction whereby the materials set to a pre-determined shape, the aforementioned indurating process is conducted to produce the final product. A desired improvement upon this process would substantially reduce the time required to preliminarily react the siliceous material and binder or accelerate the pre-setting time and which would also reduce the weight of the block without any substantial reduction in strength.

It is an object of this invention to produce a novel, light Weight siliceous material which is particularly suitable as high temperature insulating material or in the manufacture thereof.

it is a further object of the invention to provide a novel siliceous material prepared from diatomaceous earth, silica flour, and the like, which material is more suitable as a filter aid, filler, insulating material, catalyst base, and abrasive than the starting material.

It is a further object of the invention to provide an improved light weight siliceous material of increased reactivity with respect to calcareous and other silica-reactive binders and which is adapted to the manufacture of improved calcareous siliceous heat-insulating materials.

It is still a further object of the invention to provide a process for the manufacture of improved siliceous materials from minerals such as diatomaceous earth, silica flour, and other siliceous materials which are reactive with alkaline earth compounds.

It is still a further object of the invention to provide a process for the manufacture of an activated siliceous material from diatomaceous earth, a silica flour, and vesiculated, rhyolitic materials, and the like, which renders said materials highly reactive with alkaline earth silicate-producing compounds.

The above objects as well as others which will become apparent upon a complete understanding of the invention as hereinafter fully described are accomplished by reacting a composition comprising finely divided silica or siliceous material with an alkaline earth silicate-producing compound reactive with said composition, acidifying the resulting product with an acid which will be soluble in water or in the acidic medium employed during acidification while maintaining the pH during the acidification at a value between about 3.0 and about 8.0. The acidification step is then followed by recovering the resulting siliceous product in a manner hereinafter described.

In a broad embodiment of the invention, we react a finely divided silica-containing material of the type more particularly subsequently described herein with an alkaline earth silicate-producing compound, preferably a compound of lime which is reactive with silica and certain other siliceous materials at a temperature and for a time suificient to cause the formation of hydrous alkaline earth metal silicate upon the exterior surface and in the interstices of the siliceous material. The resulting composition is then acidified with an acid which will react with the hydrous alkaline earth silicate to produce a compound or salt which is soluble either in the acidified mixture or in water or in other suitable solvent. The pH of the reaction mixture is maintained between about 3.0 and about 8.0 during the acidification to insure reaction of the hydrous alkaline earth silicate with the acid agent and to prevent substantial solution of silica. This results in the formation of a siliceous aggregate having in varying amounts at base substantially that of the starting material, and which is further characterized by a reactive silica coating integrally bonded to the surface and interior surfaces of each particle. This renders the aggregate highly reactive, particularly towards calcareous binders of the type employed in the manufacture of siliceous-calcareous high-temperature insulation. Our improved siliceous products are to be distinguished from certain silicic acid-aggregate compositions consisting of silicic acid which has been precipitated from a solution of a water soluble alkali metal silicate by means of a mineral acid in the presence of a mineral aggregate such as rock, shale, diatomaceous earth, etc. Such products are characterized by a loose bonding of the silicic acid to the aggregate and the resulting coating does not form an integral and fixed part of the particle.

The siliceous materials which we employ are preferably of a particle size less than 200 mesh and may consist of siliceous shale, silica fiour, crushed siliceous rocks, silicic acids, silica gels, also diatomaceous earth (kieselguhr, infusorial earth) in a crude state or which has been calcined either with or without the use of fiuxing agents such as soda ash, sodium chloride, etc. We have also found that artificial or natural pozzolans including calcined shales, volcanic magmas, fly ash, sands, etc. which contain substantial quantities of silica either in an amorphous or colloidal state are useful for the purposes of this invention. Also certain rhyolitic minerals in an expanded state such as vesiculated perlitic minerals, pumic, volcanic ash, etc. have been found to be particularly useful inthe preparation of our improved siliceous products. Micaceous minerals such as exfoliated vermiculite are also useful when the reaction is carried out in the presence of an alkali metal compound as hereinafter described.

In conducting the initial reaction to prepare an alkaline earth silicate-siliceous aggregate, we react a silica or siliceous composition of the type-above described with'sparingly soluble basic compounds such as compounds of alkaline earth metals, either with or without the presence of an alkali metal compound such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, etc. Compounds which have been found to be particularly useful in conducting our process are the oxides and hydroxides of calcium, barium, magnesium, strontium, and the carbonates and bicarbonates of such metals. The amount of alkaline earth metal compound is preferably between about and about 100% by weight based on the weight of siliceous material. When the carbonates and bicarbonates are employed, we have found it to be particularly useful to employ the aforementioned alkali metal compounds which presumably act as catalysts or alkaline earth metal carriers and considerably accelerate the reaction between the alkaline earth metal compound and the siliceous aggregate. When alkali metal compounds are employed, we have found it to be the preferable practice to use about 0.5 to about 10.0% by weight of alkali metal compound based upon the weight of siliceous aggregate.

Following the reaction between the siliceous aggregate and the alkaline earth silicate-producing compound, the resulting reaction product is acidified with an acidic compound which will give a water soluble alkaline earth compound. In other words, the acid will react with the alkaline earth metal silicate present on the surfaces of the siliceous particles to form a compound which will be soluble either in the acidic medium or in a solvent for the resulting alkaline earth metal compounds. For the majority of the alkaline earth metal silicate-siliceous compositions, we have found that acids such as acetic, hydrochloric, sulfurous, and nitric acids and the anhydrides of such acids and mixtures of these materials are particularly suitable. Following acidification, it is the preferable practice to wash the resulting siliceous product until it is substantially free from acid and soluble salts.

The products produced according to our invention have particular utility as an aggregate for high temperature insulation and cements, especially in conjunction with calcareous binders in the manner herein described. Due to the uniformity of the active siliceous surface of the particles, the products are more useful as filteraids than the silica materials from which they were prepared; notable improvements in rate of filtration for a given clarity of filtrate are consistently observed.

Our novel products are adapted to the production of a superior light weight concrete containing Portland cement and pre-determined amounts of our active siliceous compositions. This is due to the fact that these compositions exhibit many times the reactivity of conventional pozzolanic materials such as diatomaceous earth, fly ash, etc. Alternatively, we may prepare a mixture of cement, a siliceous material or aggregate of the type contemplated herein, and an alkaline earth compound which will produce alkaline earth silicates when substantial quantities of water are added to the dry admixture. Such a cement will have better weathering characteristics and strength than those employing conventional possolanic or alkaline absorbing agents and further contribute to the strength of the cement. We may also prepare a mortar comprising essentially a substantially anhydrous mixture of one or more of our improved siliceous products with a calcareous binder, for example lime. Water may be added to this mixture as desired.

We have found that our improved siliceous materials also find utility as a base for catalytic compositions. More particularly, we may impregnate our improved siliceous products with a metal compound, such as by saturation by means of a water solution, followed by drying and heating the resulting impregnated silica at elevated temperatures in either an oxidizing or reducing atmosphere to precipitate metal oxides or metals upon the surface and in the internal structure of the silica particles. Due to the increased porosity of our siliceous materials, a more uniform coating of the metal oxides or metals may be obtained. Such compositions find particular utility in fluidized systems, for example in the catalytic cracking, reforming, alkylation, etc. of hydrocarbons.

In a specific embodiment of the invention, a crude diatomaceous earth having a particle size less than 200 mesh is reacted in an aqueous slurry with a calcium compound such as lime which may be in the form of Ca(OH)2, quick lime, hydrated lime, etc. The amount of lime or other alkaline earth silicate-producing compound is about 10 to about 100% by weight based upon the weight of diatomaceous earth, and preferably 25 to by weight, The slurry of diatomaceous earth and calcium compound is heated with agitation at elevated temperatures, preferably between about 85 C. and the boiling point of the reaction mixture until the reaction is substantially complete. The progress or rate of the reaction can be followed by pH measurements and will be complete when the pH remains constant. Upon acidification of the resulting mixture with an acid, preferably hydrochloric or sulfurous acids, HCl gas, S02 gas, or mixtures of these materials, while maintaining the pH of the mixture between about 3.0 and about 8.0 and preferably between about 4.0 and about 6.0, a siliceous product is produced which will have a bulk density from 30 to less than that of the starting material, and whose reactivity towards calcareous binders of the type conventionally employed in the manufacture of high-temperature, siliceous insulating material will be greatly improved. Another way of expressing the aforementioned improvement in bulk density is by referring to the settled volume of our improved products. This value is determined by suspending the product in water either after drying the same or by suspending the acidified wet product in water. More particularly, we have found that our improved and active diatomaceous earth products have a settled volume of between 5.0 to 11.0 cc. per gram. The lower values are for the materials which have been preliminarily dried at 120 C. prior to measuring the settled volume. As mentioned in our copending application Ser. No. 138,254, filed January 12, 1950, it is desirable to employ the active product directly or in a wet state, i. e., without drying, and reacting it direcly with a calcareous binder. Such wet products have a settled volume between 10 and 11,

cc. per gram. We have found that a product which has been produced from diatomaceous earth in accordance with our invention will react with a calcareous binder in from one-fourth to one-half the time required when using crude diatomaceous earth. The siliceous product is recovered from the acid mixture by decantation, filtratration, or centrifugation or any other suitable method and is preferably washed with water or dilute acid to substantially remove alkaline earth metal salts. In the event that sulfurous acid or S02 have been employed.

during the acidification step, it is the preferable practice to wash the product with sulfurous acid having a pH of between about 1.0 and about 4.0 to remove occluded solid alkaline earth metal sulfites since the solubility of these compounds, particularly calcium sulfite, is much greater in sulfurous acid than in water or slightly acid solutions.

We have found that when the pH of the mixture during acidification is controlled between about 3.0 and about 8.0, preferably 4 to 6, there is no danger of losing substantial quantities of silica by solution in the highly acid washing liquid, since the highly active silica is continuously converted to an insoluble form during the acidification.

The siliceous product prepared as described above may be dried at temperatures in excess of 220 C. to remove substantially all of the free water and then used as a siliceous aggregate in the manufacture of high temperature calcareous-siliceous insulation. As described in our copending patent application S. N. 138,254 filed concurrently herewith, we prefer to retain the siliceous product in a wet state and use it directly in the manufacture of the aforesaid heat-insulating material. We have found that the reactivity of the siliceous product in a wet state is considerably improved over that of the material which is dried substantially free of moisture.

To prepare a high temperature insulating material, we

admix in aqueous media our improved siliceous aggregate sulting insulating material is. to be subjected. to excessive temperatures under which conditions the organicfibers tend. to. decompose. Fibers such as asbestos, rock wool, g1asswool,. and the. like: have been found to be particularly suitable. The fibers are addedto the initial siliceous material which is'to be; reacted with the alkaline earth metal silicate-producing compound and/or are added during the following acidification and prior to the subsequent pre-setting; or hardening operation with a. calcareous binder. However, the preferred practice isto incorporate the fiberinto the desired active siliceous material and admix the resulting. composition with the calcareous binder. The fiber is, preferably present'in an amount betweenabout 5. and about 5.0% by Weight of the aggregate. In many instances, itis preferable to add a small quantity of alkali'rnetal compound such as the hydroxides of sodium or potassium, usually not in excess of 5% by weight of the active siliceous aggregate (dry basis). In addition, we may add an agent of thetype hereinafter described which will stabilize or suspend the dried solid products in water to prevent segregation or settling ofthese materials prior to hardening of the reaction mixture. Since our siliceous materials have greatly improved reactivity with respect to the calcareous binders, we admi-x the aforementioned ingredients quite rapidly, i. e., in about 2 to 3 minutes, preferably mixing the dry solid reactants together followed by addition of hot water in an amount equal to between about 100 and about 600 parts by weight based on the weight of total'solid ingredients. The resulting, slurry is then poured into molds or dies of suitable or desired shape and the molded slurry isheated at'a temperature in excess of about 85 C. under conditions whichwillprevent substantial evaporation of the water from the slurry, preferably at 100% relative humidity. When high temperatures, such'as between 100 and 150 'C. are employed, the pressure mustbe such that bubble formation is substantially prevented. This is achieved by confining the molds in a closed vessel or bypassing water vapor over the surface of the molds during this heating step. The molded slurry will set up? and harden in from 2 to -30 minutes, depending upon the temperature and'pressure conditions and upon the reactivity of the active siliceous aggregate which. in turn.

is dependent upon the material from which it hasbeen produced. Following this hardening step,the'resulting product is subjected-to an indurating process whereby the calcareous-siliceous body is heated at elevated temperatures and at high humidity to further effect a reaction between the binder and siliceous aggregate. Steam pressures of up to 300 lbs/sq. in., and temperatures between 100 and 230 C. and a reaction time of. one to six hours have been found to be useful in effecting this step of the. process. If desired, the indurated product is subsequently heated to 120C. to remove substantially all of the water therefrom.

In a further embodiment of the invention, silica flour (amorphous oracrystalline) having a particle size less than 250 mesh is reacted with calcium oxide, the latter being present inan amount between 10 and about 100% by weight based on the silica. An aqueous slurry of the. reactants is heated and agitated at the boiling; point of the mixture for a period of time between about 1 and about 4' hours. The resultingmixture is. then acidified with hydrochloric acid while maintaining the pH of the mixture between about 4.0 and about 810. The

siliceous product is isolated by filtration and is washed.-

substantially free of calcium chloride. by continued washing with water. By means of a penetration test tobe hereinafter described, we have found that such a siliceous products reacts with a calcareous. binder in about A; to /s the time required to react the original silica flour with such binders. We have found thatour active silica flour, when. mixed with about 50% by weight of lime, and water. in an amount between about 50 and-200 parts. by weight of'the solid reactants, can be poured intoslabs or'hollow cylindrical or any other desired :shapes and: the mixture hardened in about M the time required for untreated silica flour. The resulting hardened shapes may then be dried and used directly for insu'lation'pun poses, or may be autoclaved with" steam at temperatures between-I00 and 200 C. to effect further hard'ening metals, alsographite,.,amorphous carbon, etc.

andzstrengtheniiigof the structures. .Alternatively, fibers have been incorporated: into; the: active silica flour-cal careousv slurry to; strengthen, the final. shape. Asbestos ofthe Amosite grade or the long-fibered variety-is-particularly suitable for this. purpose.

We have; found that we can incorporate certain-fillers intoour heat. insulating materials and this may be. done either by having such fil=lers present during the initial reaction between" the siliceous aggregate and the alkaline 1 earth metal silicate-producing compound. or by adding,

the aggregate to the-active siliceous product producedby acidification. Fillers which have been; found to. beuseful are whiting, diatomaceous. earth which may be .either natural or calcined, silica flour, clays,..an.d various. shales and. sands in a natural or calcined state, pumice,..ex-

panded or vesicu lated rhyolitic minerals, exfoliated-yen micu'lite, etc. The fillers wili preferably comprise-the. minor. portion of the totalsolids or siliceousaggregate which is to be reacted-witlra calcareous binder.

in forming the high-temperature.insulating blocksby reacting a slurry of our improved. siliceous. aggregate: with a. calcareous binder with or without. the addition .of fibers, we. may employ stabilizing; agents such as-bentonite, montmorillonite, attapulg-ite, alum,yand thelike. This practice perm-its. greater quantities of waterto. be .used

in making the siliceous-calcareous slurries and results. in pre-hardened shapes of lower density. In many instances we. are able to dispense with the. use. of such agents due to..the. increased bulk, volume of our active. siliceous materials as. compared to the untreated or conventional aggregates.

It is also within the. scope of our invention to. prepare water-repellant. calcareous-siliceous compositions by. in.-- corporating in the. slurry which is to be pre-set. or

hardened certain water repell'ant compositions such as red oiLcasein, aluminum sulfate, asphalt. and tar .em-ulsions, .etc. Alternatively, we may coat the pre-setor induratedslabs or sheets. with organic. or inorganic .coating. materials including water-proof paper, fiber board, metal sheeting, for example copper, aluminum and steel, or with water-proof plywood. If, it is. desired to.color the. blocks, various. substances can be. added to. the. siliceous-calcareous mixture. Examples. of such substances are the oxides of iron, manganese, cobalt, anc} other '11 certain cases it will be desirable to color the face or surfaces of the final. product, and this may be accomplished by impregnation. with a suspension of white lead, barium sulfate, zinc sulfate or other pigments including iron oxide, and 'thevarious organic ultra marines, basic and acidic dyes. Additional methods for accomplishingthisfeature will occur. to those skilled in the. art.

We have also found that we can incorporate-adhesives and cements into our novel siliceous compositions, thereby either forming a loose aggregate which-resists settling or segregation when used as loose-fillinsuiation. or which can be consolidated to form r i'gidsi-liceous shapes whichare useful in high-temperature insulation. Forexample, we'may add 'Portland'cement, magnesium oxychloride, magnesium oxysulfate, or water "glass and the like touour lightweight siliceous materials and depending upon the end use theresulting, product may be formed either bymolding or CXll'llSlOIlxintO desired shapes. Alternatively, we may, if desired, employorganic binders or adhesives such. .as tars and pitches of'bitumi'nous or petroleum origin, particularly asphalt emulsions employing between about 2 and about 25% by weight of asphalt (one solid basis) based upon the weight of siliceous material. When such a composition is formed' and d'riedto remove the-water from t the emulsion, there results a rigid, strong, shaped siliceous body which is water-repellant and which is highly useful as insulating material under humid conditions.

In many applications it. is desirable to employ a 'finely divided'aggregate as a filler or extender for plastic com- 'positions, for example in natural or: synthetic rubber formulation and in synthetic plastic materials of the polyvinylchloride, phenol-formaldehyde and urea-formaldehyde type. In such cases it is preferable that the surface of the aggregate-be hydrophobic in character in order that the rubber or plastic material may wetthe particles. We have found it to be useful to employ certain agents which are usually insoluble in water, for example metallic stearates such as magnesium, aluminum andsodi'um stearate, natural andsynthetic waxes,'fatty acids -andsimilar agents.

7. It'is also within the scope of our invention to produce highly purified active siliceous compositions by any of several methods involving the preliminary separation of impurities from diatomaceous earth, silica flour or other siliceous materials as for example by air or wet classification, which may be followed by the reaction with an alkaline earth metal silicate-producing compound. The density of calcium silicate approximates 3.0 grams per cc. whereas the impurities found in diatomaceous earth as well as in other impure silica materials will average between about 1.8 and about 2.7 grams per cc. By reacting the siliceous composition with an alkaline earth silicate-producing compound, we may effectively increase the density of the silica fraction. The impurities which do not react may then be removed by wet classification methods or the calcium silicate coated silica may be removed by air classifying the dry reaction product. The purified calcium silicate coated material is then acidified according to procedures described herein to produce an active silica in a high state of purity. Such materials have been found to be useful as filteraids for solutions of pharmaceutical compounds wherein it is desired to maintain such solution free from extraneous impurities.

In order to more fully illustrate the nature and character ofthe invention but with no intention of being limited thereby, we particularly set forth the following:

In Examples 1 to 5, 100 parts by weight of diatomaceous earth, 90% of which was -250 mesh, were reacted with 50 parts by weight of lime having a purity of about 95% in sufficient water to form a slurry of low viscosity. The mixture was boiled with vigorous agitation for about four hours. Following this, the supernatant liquid was decanted and the product divided into three parts, each of which was acidified with hydrochloric acid until the pH value of the mixture reached a pre-determined point. Each sample was filtered and washed with water to substantially remove soluble salts and excess acid. Several samples were then dried in an oven at 120 C. for eight hours and ground to pass a 250 mesh screen. A portion of the material produced by aciidfication to a pH of was not dried (Example No. 1) in order that the reactivity of such a product with respect to a calcareous binder could be compared to the dried product. The reactivity of the resulting active siliceous product towards a calcareous binder was tested by admixing the products with 50% by weight of lime and adding to the resulting mixture a pre-determined amount of water so regulated that the various mixtures had substantially the same viscosity (constant consistency). The slurry was heated to a temperature of about 85 C. within two minutes with vigorous agitation and the mixture poured into a mold which was maintained at the aforesaid temperature. To measure the rapidity of pre-set" or hardening of the mixture, penetration tests were made at regular intervals by means of a penetrometer. The instrument employed was one obtained from the Precision Scientific Company with a standard 1 mm. conical tipped needle to which was applied a 150 gram load. The needle was adjusted so that it barely touched the surface of the block. Readings on the penetrometer were taken until a constant penetration of about 4 mm. was obtained.

Figure I of the drawings graphically illustrates the effect of conditioning the diatomaceous product in accordance with the present invention, the curves being numbered to correspond with the examples as set forth in Table I below. Example No. 4 is untreated diatomaceous earth.

TABLE I Comparison of treated and untreated diatomaceous earth Based on the penetration figures, the pre-set time of diatomaceous earth with 50% hydrochloric acid to pH 5 to 7 is /3 to /a of that neceslime and acidified with sary when employing untreated diatomaceous earth. Fur.- thermore, it will be seen that diatomaceous earth activated by treating with lime in accordance with the present invention and acidified with hydrochloric acid exhibits apparent bulk densities up to 50% lower than that of the untreated material.

In the following examples, employing the operations and the diatomaceous earth illustrated in Examples 1 to 5, the diatomaceous earth was reacted with 30% by weight of lime and acidified with hydrochloric acid to a pre-determined pH value. For basis of comparison, untreated diatomaceous earth (Example No. 4) and diatomaceous earth treated with 50% lime and acidified with hydrochloric acid to a pH of 5 (Example No. 1) are also illustrated. The reactivity of the active siliceous product as measured by penetration tests is graphically illustrated in Figure 11 of the drawings and the data including cake.

density of the hardened or set blocks are set forth in the following table:

TABLE II WPercent C ater conake Den- \Teutrah- J tent of sity, #Ift. Fxample Slurry for (block dried zatfim constant at 120 C.) p consistency It will be seen that reacting diatomaceous earth with 30% by weight of lime based on the weight of diatomaceous earth and acidification with hydrochloric acid produces a siliceous material slightly less reactive than when usmg 50% lime. Based on the penetration tests; the pre-set t1me of diatomaceous earth activated with 30% limewhen acidified with hydrochloric acid is /2, of that required when employing the crude diatomaceous earth.

In the following examples, an active diatomaceous earth produced in accordance with the process described for Example I was admixed with pre-determined amounts of the untreated diatomaceous earth. This mixture was reacted in an aqueous slurry with 40% by weight of lime and penetration tests were conducted as previously de-' TABLE III 1 Percent Witter;j (21}11- Ozkeagdeu- Percent en o si y it. Treated Example slurry for (blocl: dried diatomaceous constant at 120 C.) earth consistency It will be seen that the pre-set time required for the treated diatomaceous earth is used. Reducing the quantity of conditioned diatomaceous earth to 50% and 25 correspondingly increases the time required to set the siliceous-calcareous mixture.

Example No. 11

ceous material is 200% more reactive with respect to calcareous binders than the original starting material.

Our invention, therefore, makes available to the industry'a considerable quantity of impure diatomaceous earth which heretofore has been discarded but which can starting silica material. In the following table,

Example 19 is untreated silica sand.

now be utilized in the manufacture of high temperature TABLE V calcareous-siliceous insulation. I

One hundred gram samples of amorphous silica flour k (325 mesh and bulk density 0.551 gram per cc.), and Examp e Percent Percent Dgi s i v iii ii tii expanded perlite having a bulk density of 0.066 grams NEOH H20 #fiw" (dried at (minutes) per cc. before grinding and a bulk density of 0.158 grams per cc. after grinding and sieving through a 250 mesh screen were used in the following preparations: A 200 50' 32.3 210 sample of each type of material was heated inan aque- 200 49 27.8 53 ous slurry with 50% by weight of lime and 0.5% by 200 25 weight of sodium hydroxide based on the weight of siliceous material, the heating being conducted for 4 In some instances, it has been found to be advanhours at lbs/sq. in. steam pressure. The resulting ta'geous to mix various types of siliceous materials material was acidified with hydrochloric acid to a pH either prior to the initial reaction with an alkaline earth of 6, filtered, washed with water, and dried'at 110 C. or amphoteric metal compound to condition the siliceous The reactive materials weremixed with bentonite, lime, material, or alternatively, to add different types of consodium hydroxide and asbestos in the following pro- 20 ditioned siliceous material to a calcareous binder to potions: siliceous material 53%, bentonite 2%, lime form a pre-set, high-temperature insulating material. It 34.5%, sodium hydroxide 0.5%, Amosite asbestos 10%. is also useful to prepare mixtures of conditioned siliceous The reactivity of the siliceous materials as indicated by material and certain untreated siliceous or silica-conthe penetration test (50 gram load) is set forth in Figtaining aggregates to provide insulating blocks of preure IV of the drawings and in the Table IV below. Exdetermined density and strength. amples l2, l4 and 16 employ untreated siliceous ma- While the above examples illustrate the use of various terial and Examples 13, 15, and 17 employ activated forms of finely divided silica in a reaction with lime or materials produced from silica flour, expanded perlite and magnesium oxide, it is to be understood that the process ground expanded perlite, respectively, according to our may be conducted with alkaline earth metal-producing i ve tio compounds of the type previously mentioned herein, and

TABLE IV e titiitiie? Content of #lft Pre set 1bs,/1n. Example N0. siliceous Material Slurry at (block tune (Minafter auto dried at utes) Constant C claving at Consistency 125 p. s. 1.

silica flour 200 41.1 155-165 236 12 (treated) 200 28.1 10-12 205 expanded per-lite. 467 15. 1 130-155 24. 2 14 (treated) 337 14.0 -55 27.1 expanded perlite 250 25.5 -80-90 75.9

(groun 16 (treated) 250 25. 0 25-35 43. 2

Example N0. 18 1may olr may not be accomplished by the use of ta promoters. Fifty grams of dlatomaceous earth of the type ema a 1 me ployed in Examples 1 to 5 were heated in an aqueous ag i g g g g g gs the nature and character shiny 50 i of ilg Oxlde at.the f i i 1. A process for greatly increasing the surface area 38;; gfg gg at??? i gi: and reactivity to lime of diatomaceous earth which comc'hloric acid to 'a pH of about 6.0. The resulting conpus-es hea'tmg Wlth agltatlon an aqueous-slurry of finely siliceous rodupt recovered in marl 100% divided diatomaceous earth particles with from 10 to y 100 parts by weight, based upon said earth, of reagent yield, was found to react with calcium oxide to form a l taken from the group consistmg of the oxides, hydroxides, i q i g reflulred g gb 1/2 of carbonates and bicarbonates of an alkaline earth metal t at require W empgymg untreate atomaceous to produce a coating of alkaline earth metal silicate upon g ii i g gg g silica Sand was ground so the exterior surfaces and interstices of the diatomaceous that about 90% would a a 325 mesh Screw one ii=i3io?i yi?;chiii i% t2;oifilii iuiiiaiiiiiifiii f ggd fi g gg s gfi g iig iii 22 1253 32; of the alkaline earth metal and leave a reactive silica With suflicient water to provide a reaction mixture of l i mtegrany bonded on Sald Parades Whlle m fairly low viscosity. In order to accelerate the reaction, i g h pH fi i fi t5 about during a small quantity of sodium hydroxide (in amounts as 1 Canon a mg 6 resu mg 31 pm to indicated in Table V) was added. The resulting mixmove.excess. acld p 9 salts and recovermg the tures were boiled for a period of four hours and then resultmg Sohd reacnve slhcaproduqt acidified with hydrochloric acid to a pH of about 6.0. A PF F greatly. tncreasmg h Surface area The resulting siliceous Product was dried at and reactivity to l1me of 8111660118 material taken from and its reactivity towards calcareous binders was tested the Conslstmg 9 slhceous Shales and P F s1l1ca in the following manner sand, s1l1ca flour, diatomaceous earth, artificial and Seventy parts of each of the treated silica materials f POZZQIaHS, and P Y P were admixed with 45 parts f lime 1 parts f minerals which comprlses heatlng with ag tat on an bestos, 2 parts f b m i 0 6 part of di b 70 aqueous slurry of finely divided partlcles of sa d siliceous droxide (based on the weight of active silica). To the aterlals Wltll from 10 to 100 P r s y Welght, based resulting mixture was added a sufficient amount of water p Sald 81111369118 mateflali 0f g P taken from to provide equal consistencies for the mixture. The the P P conslstlng 0f the Q hYGTOXIdeS, carbonates resulting slurries were rapidly heated to 85 C. and and bicarbonates of an alkaline earth metal to produce a maintained substantially in this temperature during the COa'EIIIg 0f 811911116 earth metal P 1 the Setting i d surfaces and 11111618111668 of the s1l1ce ous particles, acidify- The data in the following table indicate that the silica mg th s g product Wlth Suffiment hydrochlorlc acld sand treated with lime in conjunction with a small to solubilize substantially all of the alkaline earth metal quantity of alkali metal compound reacts with lime as and leave a reactive silica coating integrally bonded a binder in A to A; the time required to react the on said particles While maintaining the pH between about 3.0 to about 8.0 during acidification, washing the resulting silica product to remove excess acid and soluble salts and recovering the resulting solid reactive silica product.

3. A process for greatly increasing the surface area and reactivity to lime of finely divided silica particles which comprises acidifying a composition comprising finely divided silica which has been heated with agitation in an aqueous slurry with from to 100 parts by weight, based upon said silica, of reagent taken from the group consisting of the oxides, hydroxides, carbonates and bicarbonates of an alkaline earth metal to produce a coating of alkaline earth metal silicate upon the exterior surfaces of the silica particles, said acidification being effected with sufficient acid taken from the group consisting of hydrochloric, nitric, sulfurous and acetic acids and their anhydrides to solubilize substantially all of the alkaline earth metal and leave a reactive silica coating integrally bonded on said particles while maintaining the pH between about 3.0 to about 8.0 during acidification, washing the resulting silica product to remove excess acid and soluble salts and recovering the resulting solid reactive silica product.

4. A product having a high reactivity to lime consisting essentially of a fine particled material having a base of diatomaceous earth which is integrally coated with amorphous silica, said product having a bulk density of from 30 to 60% less than that of the base diatomaceous earth and having a settled volume of between 5.0 to 11.00 cc. per gram.

5. A product having a high reactivity to lime consisting essentially of a fine particled material having a base taken from the group consisting of silica flour and ground silica sand which is integrally coated with amorphous silica, said product having 4 to 6 times the reactivity to lime as compared with the initial silica material.

6. A process for greatly increasing the surface area and reactively to lime of silica flour which comprises heating with agitation an aqueous slurry of essentially -200 mesh silica fiour with from 10 to 100 parts by weight, based upon said flour, of reagent taken from the group consisting of the oxides, hydroxides, carbonates and bicarbonates of an alkaline earth metal to produce a coating of alkaline earth metal silicate upon the exterior surfaces and interstices of the silica flour particles, acidifying the resulting product with sufficient hydrochloric acid to solubilize substantially all of the alkaline earth metal and leave a reactive silica coating integrally bonded 'on said particles while maintaining the pH between about 3.0 to about 8.0 during acidification, washing the resulting silica product to remove excess acid and soluble salts and recovering the resulting solid reactive silica product.

7. A process for greatly increasing the surface area and reactively to lime of diatomaceous earth which comprises heating with agitation an aqueous slurry of finely divided diatomaceous earth particles with from 10 to 100 parts by weight, based upon said earth, of reagent taken from the group consisting of the oxides, hydroxides, car bonates and bicarbonates of an alkaline earth metal to produce a coating of alkaline earth metal silicate upon the exterior surfaces and interstices of the diatomaceous earth particles, acidifying the resulting product with sulfurous acid to produce alkaline earth metal sulfite and leave a reactive silica coating integrally bonded on said particles while maintaining the pH between about 3.0

'12 to about 8.0 during acidification and washing the resulting product with sulfurous acid having a pH between about 1.0 and about 4.0 to remove residual alkaline. earth metal sulfite from the reactive silica product.

8. A process for producing a reactive silica product Which comprises heating with agitation an aqueous slurry of essentially 200 mesh silica flour with from 10 to 100 parts by weight of lime, based upon said silica flour, to produce a coating of calcium silicate upon the exterior surfaces and interstices of the silica flour particles, acidifying the resulting product with sulfurous acid while maintaining a pH between about 4.0 and about 8.0 during acidification thereby producing calcium sulfite and leaving a reactive silica coating integrally bonded on said particles, washing the resulting product with a solvent for calcium sulfite and which is substantially inert to silica, and recovering the resulting solid reactive silica product.

9. A process for greatly increasing the surface area and reactivity to lime of silica sand which comprises heating with agitation an aqueous slurry of essentially 325 mesh silica sand with from 10 to 100 parts by weight, based upon said sand, of reagent taken from the group consisting of the oxides, hydroxides, carbonates and bicarbonates of an alkaline earth metal in the presence of between about 0.1 and about 10% by weight of alkali metal hydroxide, to produce a coating of alkaline earth metal silicate upon the exterior surfaces and interstices of the silica sand particles, acidifying the resulting product with sufficient acid taken from the group consisting of hydrochloric, nitric, acetic and sulfurous acids and their anhydrides to solubilize substantially all of the alkaline earth metal and leave a reactive silica coating integrally bonded on said particles while maintaining the pH between about 3.0 to about 8.0 during acidification, washing the resulting silica product to remove excess acid and soluble salts and recovering the resulting solid reactive silica product.

10. A process according to claim 9 wherein the reagent employed to produce the alkaline earth metal silicatecoated sand particles is lime and the acid is sulfurous acid.

11. A process according to claim 9 wherein the reagent employed to produce the alkaline earth metal silicatecoated silica sand particles is lime and the acid is hydrochloric acid.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 685,094 Bowie Oct. 22, 1901 1,060,614 McCarty May 6, 1913 1,590,132 Teitsworth June 22, 1926 1,798,766 Stoewener Mar. 31, 1931 1,874,186 Guertler Aug. 30, 1932 1,945,534 Rembert Feb. 6, 1934 2,062,879 Hammenecker Dec. 1, 1936 2,215,891 Thomson et al Sept. 24, 1940 2,249,767 Kistler July 22, 1941 2,258,787 Melaven et al. Oct. 14, 1941 FOREIGN PATENTS Number Country Date Great Britain May 14, 1898 of 1898 375,144 Great Britain June 23, 1932 

4. A PRODUCT HAVING A HIGH REACTIVITY TO LIME CONSISTING ESSENTIALLY OF A FINE PARTICLED MATERIAL HAVING A BASE OF DIATOMACEOUS EARTH WHICH IS INTEGRALLY COATED WITH AMORPHOUS SILICA, SAID PRODUCT HAVING A BULK DENSITY OF 